The major focus of research activity this year is directed toward summarizing the long- term psychophysical and electrophysiological findings in GA, which in some cases is as long as 20 years. Of continuing interest is the question of whether the long-term reduction of plasma ornithine levels using an arginine restricted diet in patients with GA will slow the progression of the chorioretinal degeneration. To answer this question, a natural history of two pairs of young sibs with GA, treated with an arginine restricted diet, was conducted for 16 to 17 years. Outcome variables included fundus photography as well as electrophysical and psychophysical retinal function tests. A comparison of the younger sib started on diet at an earlier age than the older sib demonstrated what appeared to be a different phenotype and a slower progression of the lesions in the younger as compared to the older sibling. It was concluded that if the diet was begun at an early age, long-term substantial reduction of plasma ornithine changed the appearance and slowed the progression of the chorioretinal lesions and, to a lesser extent, the progressive loss of retinal function in patients with GA.